The present invention relates to an aircraft. In particular, the aircraft may be one capable of hovering, such as a helicopter or convertiplane.
As is known, helicopters comprise at least one hydraulic circuit; and a number of actuators operated by the hydraulic circuit, and some of which perform essential functions, such as in-flight attitude control, e.g. control the attack angle of the main and/or tail rotor blades. In the event of a malfunction, particularly a fall in pressure to the actuators, the blade attack angle is no longer fully controllable, and the attitude of the helicopter may be seriously impaired.
A fall in hydraulic circuit pressure may have any number of causes. For example, an aircraft normally evolves over a long period of time and a long working life, in the course of which, it is invariably upgraded with new equipment and actuators that must be connected to the existing hydraulic circuit. Though this is designed and certified to allow for such upgrading, original design criteria may sometimes prove poorly conservative, on account of the long working life of the aircraft, rapid developments in technology, and increasing customer demand for better performance.
As a result, the hydraulic circuit as originally designed and certified may be unable to supply actuators with the necessary pressure in all possible operating conditions of the aircraft.
One possible solution is to redesign and recertify the hydraulic system. But this would involve considerable time and money.
A need is therefore felt within the aircraft industry for some way of upgrading aircraft hydraulic equipment, while avoiding the time and cost involved in designing and certifying an upgraded hydraulic system.